The identification of natural, synthetic, and laboratory-treated gemstones presents an ongoing challenge to gemologists and jewelers. To address this problem, practical instruments are needed that will enable gemstones to be distinguished from one another quickly and easily.
Gemologists have traditionally used the visible spectra of gemstones to help in their identification. When light passes through a gemstone, a portion of the visible spectrum of a gemstone may be observed by means of the spectroscope enabling a viewer, to see the pattern of sharp absorption lines and broad regions of absorption and transmission that are often characteristic of a particular gem material.
This invention uses a selective filter to distinguish two different gemstones that may be similar in color, but differ in their visible spectra. One embodiment of the invention comprises:
a) a light source;
b) a glass plate on which the gemstone is placed for observation;
c) an iris diaphragm to restrict light from being transmitted around the edge of the gemstone being examined;
d) a selective filter, chosen depending upon the spectra of the two gemstones to be distinguished;
e) and a lens to view the gemstone in transmitted light.
By means of this invention, and the proper selection of the filter, it is possible to directly observe whether or not a gemstone is transmitting the light passed by the filter. By proper selection of the filter, one gemstone will appear to transmit the light, and it will appear bright, while the other gemstone will not transmit the light, and it will appear dark. The idea of gem identification by using filtered transmitted light is one novel aspect of the invention. The apparatus also provides for a convenient and expedient gem identification process.
There are several possible applications of this invention. Specific applications include distinguishing:
a) type-I a colorless diamonds which occur in nature from type-ii-a colorless diamonds (which are rare in nature and can be produced in the laboratory). For this application, the invention will make use of a bandpass filter with a center frequency of about 415 nanometers. The type I-a colorless diamonds will transmit this light and thus appear bright in the viewfinder. In contrast, a type II a colorless diamond will appear dark. Such a test will allow jewelers to quickly determine whether further evaluation for synthetic diamond material is required;
b) diamonds that have been treated with a high refractive index glass to hide the visibility of surface-reaching fractures from non-treated diamonds. Diamonds that have been treated with a high refractive index glass have an altered absorption pattern compared to untreated diamonds. The transmission based gem detection system described herein deploys a band-pass filter which selects for high refractive index glass;
c) colorless diamond from colorless synthetic mossanite (silicon carbidexe2x80x94a new diamond imitation material). For this application, this instrument deploys a filter which filters out light at wavelengths above about 430 nanometers. Diamond is relatively transparent in this region below 430 nanometers, while moissanite is more opaque and light absorbing for this region. Thus, when the selective filter permits illumination of the gem only with light below 430 nanometers, the diamond appears bright through the viewer. The moissanite appears dark under the same circumstances.
d) natural color gemstones from laboratory-treated colored gemstones and from synthetic colored gemstones.
No other similar gem-testing instruments are known. There are several colored lenses that are sold by Hanneman Gemological Institute of Castro Valley, Calif., that distinguish certain types of colored gemstones based upon how the gemstones appear in reflected white light when viewed through the lens. For example, such lenses may be used to separate topaz from aquamarine gems. There is also a device, known as a phosphorescope used for visual observation, and an instrument used for measurement of differences in transparency of gemstones to short-wave ultraviolet radiation. However, none of these products work on the basis of the same principle as the instrument described herein.